12.4 Code Generation for Array Aggregates

Aggregates have a rich syntax and allow the user to specify the values of
complex data structures by means of a single construct. As a result, the
code generated for aggregates can be quite complex and involve loops, case
statements and multiple assignments. In the simplest cases, however, the
compiler will recognize aggregates whose components and constraints are
fully static, and in those cases the compiler will generate little or no
executable code. The following is an outline of the code that GNAT generates
for various aggregate constructs. For further details, you will find it
useful to examine the output produced by the -gnatG flag to see the expanded
source that is input to the code generator. You may also want to examine
the assembly code generated at various levels of optimization.

The code generated for aggregates depends on the context, the component values,
and the type. In the context of an object declaration the code generated is
generally simpler than in the case of an assignment. As a general rule, static
component values and static subtypes also lead to simpler code.